The adc kennen going into bork doesn't seem unreasonable, as adc kennen does work (to the extent it does at all) through on-hit effects and attack speed synergy with his w. (I feel like gold/plat is where people will sometimes think they know what trolling is (because they think they're good at the game), and consider anything they disagree with as trolling, but OTP's and similar will proceed to stomp them with off-meta champs/roles/builds since they actually do know what they're doing and how to play them, and it often works out that the person complaining about trolling is the worst on the team since they're tilted over the 'troll'.)
Trolls and afk's are pretty much always a thing though, with maybe some brief relief in the middle of tiers. At low divisions, people are bad and salty they can't climb further (or they don't care to since they reached their tier goal for the season), so they don't feel they have much to lose. At high divisions, you get mixed with the division 5 people from the tier above, who don't care for the aforementioned reasons.
Master/challengers are gods who often have difficulties getting fair matchmaking, and so might do 'troll' picks to make things more interesting when they're high challenger players getting matched with diamonds, which might otherwise be stompy.